A multi-spool gas turbine engine comprises at least two rotating bodies. Most of the turbines are twin-spool or triple-spool, but a higher number of spools is also possible. A body is formed by a rotor that rotates about an axis, and a shaft that connects a module forming the compressor and a module forming the turbine, the compressor module being driven by the turbine module, via the shaft.
Some of the energy generated by the engine is used to drive various items of equipment thereof. Conventionally, all of the power required is mechanically drawn from the shaft of the high-pressure body of the engine, by means of a power take-off shaft that is arranged substantially radially with respect to the shaft of the high-pressure body, and is connected to a gearbox for driving accessory equipment, generally known by the term “accessory gearbox”, or AGB. The accessory gearbox is mounted in the nacelle of the engine and is connected to some equipment or accessories such as, in particular, one or more electrical generator(s), hydraulic fuel and oil pumps, and a starter motor.
There is currently a tendency to increase the supply of electrical power for the accessories, and it is therefore necessary to use generators which require increased mechanical power for their operation. Providing increased mechanical power while maintaining the operability of the turbine engine throughout its flight region requires a solution to be found other than that of drawing power from the shaft of the high-pressure body.
One solution could consist in drawing the power from the low-pressure body of the engine.
However, the engine cannot start without a preliminary phase of setting the high-pressure body into rotation. Only when the shaft of the high-pressure body reaches a sufficient rotational speed can the corresponding compressor provide enough air to the combustion chamber, for the purpose of starting the engine.
One solution therefore consists in coupling the starter motor to the low-pressure body of the engine, and allowing the low-pressure body to be coupled to the high-pressure body during the start-up phase.
Indeed, increasing the power requirements of the electrical generators also makes it possible to design electrical machines that can be used in a reversible manner in an electric motor. The power of a machine of this kind is sufficient for rotating the high-pressure body of the engine.
WO 2014/0134256 discloses a multi-spool gas turbine engine, in particular an aircraft engine, comprising at least one rotating low-pressure body, a rotating high-pressure body, and a starter motor, in which the starter motor is coupled to the low-pressure body, and in which the engine comprises a first disengageable coupling device which is interposed between the low-pressure body and the high-pressure body in order to rotatably connect the high-pressure body to the low-pressure body in order to make it possible to start up the engine by means of the starter motor.
In this document, the coupling or separation of the coupling device is determined by an inertia clutch device that is automatically separated at a pre-determined speed of the low-pressure body, the high-pressure body and the coupling device. The separation speed is thus determined by the high-pressure body, and therefore the low-pressure body may, nevertheless, be driven at speeds that are too high.